JP5939701B2 - Pneumatic tire - Google Patents

Description

  The present invention relates to a pneumatic tire capable of discharging static electricity generated in a vehicle body or a tire to a road surface.

  In recent years, for the purpose of reducing the rolling resistance of a tire that is closely related to the fuel efficiency, a pneumatic tire is proposed in which a rubber member such as a tread rubber is formed of a non-conductive rubber compounded with a high ratio of silica. However, such a rubber member has higher electrical resistance than conventional products containing a high proportion of carbon black, and inhibits discharge of static electricity generated in the vehicle body and tires to the road surface, so it is likely to cause problems such as radio noise. There is a problem.

  Accordingly, a pneumatic tire has been developed in which a tread rubber is formed of a non-conductive rubber, and a conductive rubber compounded with carbon black or the like is provided so that a current-carrying performance can be exhibited. For example, in the pneumatic tire described in Patent Document 1, static electricity is discharged by covering the paired side end portions on both sides in the tire width direction of the tread rubber formed of nonconductive rubber with the conductive rubber. A tire is disclosed in which the conductive path is configured from the tread rubber contact surface to the portion extending from the tread end.

Japanese Patent Laid-Open No. 9-30212

  However, in the tire configured as described above, the conductive rubber, which is more easily worn than the nonconductive rubber, is in a state where the grounding surface near the grounding end is covered and exposed to the surface. Compared to the center portion), the vicinity of the ground contact end is easily worn, and uneven wear such as shoulder dropping is likely to occur. Moreover, in this case, if wear is taken into consideration, the volume of the conductive rubber must be increased, and the rolling resistance is deteriorated. In addition, it is preferable to dispose rubber having excellent crack resistance on the surface near the grounding end. In the above configuration, in order to secure a conductive path, conductive rubber having poor crack resistance is disposed. As a result, the crack resistance is deteriorated.

  Furthermore, it is desirable for the tire to reduce noise generated during traveling in order to provide a comfortable ride. Since this noise is affected by the rigidity of the tread portion of the tire, it is preferable that the rigidity of such a part can be easily adjusted.

  The present invention has been made paying attention to such problems, and its purpose is mainly to reduce rolling resistance and to easily adjust the rigidity of the tread portion to reduce noise. Is to provide tires.

  In order to achieve the above object, the present invention takes the following measures. That is, the pneumatic tire of the present invention includes a pair of bead portions, sidewall portions extending outward in the tire radial direction from each of the bead portions, and a tread portion connected to an outer end in the tire radial direction of each of the sidewall portions. A toroidal carcass layer provided between the pair of bead portions; a sidewall rubber provided outside the carcass layer in the sidewall portion; and provided outside the carcass layer in the tread portion. A tread rubber, wherein the tread rubber is formed of a non-conductive rubber and forms a ground contact surface; and a base portion provided inside the cap portion in the tire radial direction. The cap portion is provided at at least one side end portion of the paired side end portions at both ends in the tire width direction, and the grounding A conductive portion that is shaped to connect the grounding surface and the side end surface or the bottom surface of the cap portion in the tire meridian cross section through the inside of the cap portion while avoiding the position of covering the conductive portion, the conductive portion, A rubber hardness that is different from the non-conductive rubber forming the cap portion, having an extending portion that branches from the conductive path connecting the grounding surface and the side end surface or bottom surface of the cap portion and extends outward in the tire width direction. It is characterized by being made of conductive rubber.

  In this way, in the tire meridian cross section, the conductive portion that becomes a conductive path that connects the ground surface and the side end surface or bottom surface of the cap portion passes through the inside of the cap portion to avoid the position covering the ground surface. Therefore, it is possible to suppress the conductive rubber that is more easily worn than the non-conductive rubber from being exposed to the surface as a ground surface, and to suppress uneven wear such as a shoulder drop. In addition, since the conductive rubber having poor crack resistance is retracted from the surface, the crack resistance can be improved. Nevertheless, since the volume of the conductive rubber is suppressed while ensuring the conductive performance, the rolling performance can be improved.

  For example, when the side end portion of the cap portion is partitioned into the tire outer side and the inner side by the conductive rubber having a hardness higher than the hardness of the cap portion, the rigidity of the side end portion is increased compared to the case where the side end portion is not partitioned, The higher order of the cross section is suppressed, and noise in the high frequency region is mainly reduced. On the other hand, when the side end portion of the cap portion is partitioned into the tire outer side and the inner side by the conductive rubber having a hardness lower than that of the cap portion, the rigidity of the side end portion is lower than that in the case where the side end portion is not partitioned. Thus, the primary eigenvalue is lowered, and noise in the low frequency region is mainly reduced. The present invention utilizes this to provide a conductive portion having an extending portion extending outward in the tire width direction so that the side end portion of the cap portion is partitioned inside and outside the tire. Therefore, just by providing such a conductive part, the rigidity of the side end portion of the cap part can be changed to a desired rigidity compared to the case without the conductive part, and noise is reduced through appropriate rigidity setting. It becomes possible to make it.

  Further, as another aspect of the present invention, a pair of bead portions, sidewall portions extending outward in the tire radial direction from each of the bead portions, and a tread portion connected to an outer end in the tire radial direction of each of the sidewall portions, A toroidal carcass layer provided between the pair of bead portions; a sidewall rubber provided outside the carcass layer in the sidewall portion; and provided outside the carcass layer in the tread portion. A tread rubber, wherein the tread rubber is formed of a non-conductive rubber and forms a ground contact surface; and a base portion provided inside the cap portion in the tire radial direction. The cap portion is provided at at least one side end portion of the paired side end portions at both ends in the tire width direction, and covers the grounding surface. A conductive portion that passes through the inside of the cap portion and avoids a position to connect the grounding surface and a side end surface or a bottom surface of the cap portion, and the conductive portion is a non-conductive material that forms the cap portion. A belt-shaped conductive rubber having a rubber hardness different from that of the rubber is arranged around the tire axis in a spiral manner from the side end surface or bottom surface of the cap portion to a position exposed to the grounding surface, in the tire meridian cross section, A pneumatic tire is characterized in that a portion exposed to the grounding surface and a portion reaching the side end surface or the bottom surface of the cap portion are divided by the non-conductive rubber forming the cap portion. Even with such a configuration, the same effect as described above can be obtained.

  In order to improve uniformity in the tire width direction (lateral direction), it is preferable that the conductive portion is provided on one side in the tire width direction and on the other side in the tire width direction. According to this configuration, since the conductive rubber is arranged in a well-balanced manner in the tire width direction, the uniformity in the tire lateral direction can be improved.

The tire meridian cross-sectional view showing an example of the pneumatic tire according to the present invention. Sectional drawing which shows typically the tread rubber before vulcanization molding. Sectional drawing which shows typically the tread rubber before the vulcanization | molding which concerns on other embodiment of this invention. Sectional drawing which shows typically the tread rubber before the vulcanization | molding which concerns on embodiment other than the above of this invention. Typical explanatory drawing regarding the manufacturing method of the tread rubber shown in FIG. Sectional drawing which shows typically the tread rubber before the vulcanization | molding which concerns on embodiment other than the above of this invention.

  Hereinafter, a pneumatic tire according to an embodiment of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the pneumatic tire T includes a pair of bead portions 1, sidewall portions 2 that extend outward from the respective bead portions 1 in the tire radial direction RD, and outer sides in the tire radial direction RD of both sidewall portions 2. And a tread portion 3 connected to the end. The bead portion 1 is provided with an annular bead core 1a formed by covering a converging body such as a steel wire with rubber and a bead filler 1b made of hard rubber.

  The tire T includes a toroidal carcass layer 4 that extends from the tread portion 3 through the sidewall portion 2 to the bead portion 1. The carcass layer 4 is provided between a pair of bead portions 1 and is constituted by at least one carcass ply, and its end is locked in a state of being wound up via a bead core 1a. The carcass ply is formed by covering a cord extending substantially perpendicular to the tire equator CL with a topping rubber. Inside the carcass layer 4 is disposed an inner liner rubber 4a for maintaining air pressure.

  Further, a sidewall rubber 6 is provided outside the carcass layer 4 in the sidewall portion 2. A rim strip rubber 7 is provided outside the carcass layer 4 in the bead portion 1 so as to come into contact with a rim (not shown) when the rim is mounted. In the present embodiment, the topping rubber and rim strip rubber 7 of the carcass layer 4 are made of conductive rubber, and the side wall rubber 6 is made of non-conductive rubber.

  On the outer side of the carcass layer 4 in the tread portion 3, a belt 4b for reinforcing the carcass layer 4, a belt reinforcing material 4c, and a tread rubber 5 are provided in order from the inner side to the outer side. The belt 4b is composed of a plurality of belt plies. The belt reinforcing member 4b is configured by covering a cord extending in the tire circumferential direction with a topping rubber. The belt reinforcing material 4b may be omitted as necessary.

  As shown in FIGS. 1 and 2, the tread rubber 5 includes a cap portion 50 formed of non-conductive rubber and constituting a ground contact surface, and formed of non-conductive rubber and inside the cap portion 50 in the tire radial direction. A base portion 51 is provided, and a conductive portion 52 that is made of conductive rubber and extends from the ground surface to the side bottom surface 50b of the cap portion 50. A plurality of main grooves 5 a extending along the tire circumferential direction are formed on the surface of the tread rubber 5. In the present embodiment, the base portion 51 is formed of non-conductive rubber, but may be formed of conductive rubber.

  In the above, the ground contact surface is a surface that is assembled to a regular rim and filled with a regular internal pressure, the tire is placed vertically on a flat road surface, and is grounded to the road surface when a regular load is applied. The outermost position is the ground contact E. The normal load and the normal internal pressure are the maximum load (design normal load in the case of passenger car tires) specified in JIS D4202 (the origin of automobile tires) and the air pressure corresponding to this, and the normal rim is As a rule, the standard rim specified in JIS D4202 etc. shall be used.

  In the present embodiment, a side-on-tread structure in which the sidewall rubber 6 is placed on both end portions of the tread rubber 5 is employed. However, the present invention is not limited to this structure, and both end portions of the tread rubber are connected to the sidewalls. It is also possible to employ a tread on side structure that is placed on the outer end of the rubber radial direction RD.

Here, the conductive rubber is exemplified by a rubber having a volume resistivity of less than 10 ⁸ Ω · cm. For example, the conductive rubber is produced by blending carbon black as a reinforcing agent in a high ratio with a raw material rubber. In addition to carbon black, carbon fibers such as carbon fiber and graphite, and metal-based known conductivity imparting materials such as metal powders, metal oxides, metal flakes, and metal fibers can also be blended.

Further, the non-conductive rubber is exemplified by a rubber having a volume resistivity of 10 ⁸ Ω · cm or more, and a rubber blended with a raw material rubber in a high ratio as a reinforcing agent is exemplified. For example, the silica is blended in an amount of 30 to 100 parts by weight with respect to 100 parts by weight of the raw rubber component. As silica, wet silica is preferably used, but those commonly used as reinforcing materials can be used without limitation. The nonconductive rubber may be prepared by blending calcined clay, hard clay, calcium carbonate, or the like, in addition to silicas such as precipitated silica and anhydrous silicic acid.

  Examples of the raw rubber include natural rubber, styrene butadiene rubber (SBR), butadiene rubber (BR), isoprene rubber (IR), and butyl rubber (IIR). These may be used alone or in combination of two or more. Used. A vulcanizing agent, a vulcanization accelerator, a plasticizer, an anti-aging agent and the like are appropriately blended with the raw rubber.

The conductive rubber forming the conductive portion 52 has a nitrogen adsorbing non-surface area: N ₂ SA (m ² / g) × carbon black blending amount (mass%) of 1900 from the viewpoint of improving durability and improving current-carrying performance. As described above, it is desirable that the blend is 2000 or more and the dibutyl phthalate oil absorption: DBP (ml / 100 g) × carbon black blending amount (mass%) is 1500 or more, preferably 1700 or more. N ₂ SA is determined according to ASTM D3037-89, and DBP is determined according to ASTM D2414-90.

  FIG. 2 schematically shows the tread rubber 5 before vulcanization molding. As shown in FIG.1 and FIG.2, the electroconductive part 52 is provided in both the side edge parts which make the pair in the tire width direction both sides of the cap part 50, and avoids the position which coat | covers a grounding surface, and the cap part 50's The shape which connects the grounding surface and the side bottom face 50b of the cap part 50 in the tire meridian cross section is formed. Specifically, the conductive portion 52 extends in the tire radial direction to connect the ground contact surface and the side bottom surface 50b of the cap portion, and an extended portion that branches from the conductive route 52a and extends outward in the tire width direction. 52b. The conductive portions 52 are respectively provided on one side and the other side in the tire width direction and are paired on the left and right with the tire equator CL interposed therebetween. Of course, in order to improve the uniformity in the lateral direction of the tire, the conductive portion 52 on one side in the tire width direction and the conductive portion 52 on the other side in the tire width direction are symmetrical with respect to the tire equator CL. It is preferable that the relationship is set.

  As shown in FIG. 2, the conductive path 52 a constituting the conductive portion 52 is grounded from a ground surface on the inner side in the tire width direction WD from the ground end E in a cross section orthogonal to the tire circumferential direction (also referred to as a tire meridian section). It passes through a region below the end E and reaches the side end face 50 a of the cap portion 50. From the viewpoint of improving the rolling performance by reducing the volume of the conductive rubber, the portion P1 where the outer end in the tire radial direction of the conductive path 52a is exposed to the ground contact surface is within 30 mm, more preferably within 15 mm from the ground contact E. It is desirable. Furthermore, it is desirable that the conductive portion 52 is disposed on the outer side in the tire width direction than the exposed portion P1. In order to further improve the rolling resistance, it is preferable that only the non-conductive rubber is disposed on the inner side in the tire width direction WD than the conductive path 52a without the conductive rubber being disposed.

  A plurality of extending portions 52b are provided along the tire radial direction RD, and branch from the conductive path 52a to reach the side end surface 50a of the cap portion 50 located outside the tire width direction WD. It can also be said that the tip of the extended portion 52b is in contact with the sidewall rubber 6 on the side end face 50a of the cap portion 50.

  The conductive portion 52 is formed of conductive rubber having a hardness different from the rubber hardness of the cap portion 50. For example, if the rubber hardness of the conductive portion 52 is made higher than the rubber hardness of the cap portion 50, the rigidity of the side end portion of the tread portion 3 is relatively increased with respect to the central portion of the tread portion 3, so the primary eigenvalue is high. As a result, the higher order of the cross section is suppressed, and noise (vibration) mainly in a high frequency region (for example, 250 to 500 Hz) is reduced. On the contrary, if the rubber hardness of the conductive portion 52 is made lower than the rubber hardness of the tread portion 3, the rigidity of the side end portion of the tread portion 3 is relatively lowered with respect to the central portion of the tread portion. Primarily, noise in a low frequency region (for example, 80 to 160 Hz) is reduced. In order to obtain such an effect, the rubber hardness difference between the cap portion 50 and the conductive portion 52 may be set to 1 ° or more, and more preferably, there is a hardness difference of 3 ° or more. . The rubber hardness here means the hardness measured according to JISK6253 durometer hardness test (type A).

  Therefore, in the present embodiment, the rigidity of the side end portion of the tread portion 3 can be set to a desired rigidity by changing the rigidity of the side end portion of the tread portion 3 as compared with the case where the conductive portion 52 is not provided only by arranging such a conductive portion 52. It is possible to reduce noise in a low frequency region or a high frequency region through an appropriate rigidity setting.

  In addition, since the conductive portion 52 that leads from the ground surface to the side bottom surface 50b of the cap portion 50 and serves as a conductive path passes through the inside of the cap portion 50 so as to avoid the position covering the ground surface, it is compared with non-conductive rubber. It is possible to prevent the conductive rubber that is easily worn away from being exposed to the surface as a ground contact surface, and to suppress uneven wear such as shoulder dropping. In addition, since the conductive rubber having poor crack resistance is retracted from the surface, the crack resistance can be improved.

  Furthermore, in the present embodiment, since the conductive portion 52 is provided on each of the tire width direction WD one side and the tire width direction WD other side, the conductive rubber is disposed in a balanced manner on both sides of the tire width direction WD. It is possible to improve uniformity in the width direction (lateral direction) of the tire.

[Other Embodiments]
(1) In this embodiment, the topping rubber and the rim strip rubber 7 of the carcass layer 4 are formed of conductive rubber, and the side wall rubber 6 is formed of non-conductive rubber. The carcass topping rubber, rim strip rubber, and sidewall rubber may be formed of non-conductive rubber or conductive rubber as long as a conductive path is formed between the rim contact portion of the strip rubber. It may be formed. The combination can be changed as appropriate.

  (2) Furthermore, although the conductive path 52a is disposed so as to reach the side bottom surface 50b of the cap portion 50 from the ground surface, it may be disposed so as to extend from the ground surface to the lower side end surface 50a of the cap portion 50. Good. Moreover, in this embodiment, although the cap part 50 is formed with nonelectroconductive rubber, you may be formed with electroconductive rubber.

  (3) Furthermore, in the present embodiment, the conductive portions 52 are provided on both of the paired side end portions on both sides of the tire width direction WD of the cap portion 50, but the conductive portions 52 are conductive only on one of the side end portions. A part may be provided. In this case, it is preferable to provide a tire that is easily grounded according to the camber when the tire is attached to the vehicle body. In general, it is preferable to provide a conductive portion at a side end located inside the vehicle body when attached to the vehicle body.

  (4) Furthermore, in this embodiment, as shown in FIGS. 1 and 2, the extended part 52 b reaches the side end surface 50 a of the cap part 50, but as shown in FIG. 3, the extended part The front end P <b> 1 of 52 b may be terminated inside the cap unit 50 without reaching the side end surface 50 a of the cap unit 50. In this case, in order to exhibit the noise reduction effect, the distance W1 between the tip P2 of the extension part 52b and the side end face 50a is preferably 15 mm or less, more preferably 5 mm or less.

  (5) Further, in the present embodiment, the conductive portion 52 has a shape connecting the ground plane and the bottom surface 50b of the cap portion 50 in the tire meridian cross section, but may have a shape shown in FIG. That is, as shown in FIG. 4, the conductive portion 152 connects the ground plane and the side end surface 150 a of the cap portion 150 through the inside of the cap portion 150 while avoiding the position covering the ground plane. A belt-shaped conductive rubber having a rubber hardness different from that of the non-conductive rubber forming 150 is spirally arranged around the tire axis from the side end surface 150a of the cap portion 150 to a position exposed on the ground surface, In the tire meridian cross section, the portion P2 exposed to the ground contact surface and the portion P3 reaching the side end face 150a of the cap portion 150 are separated by the non-conductive rubber forming the cap portion 150. Here, the case where the sidewall rubber 6 is a conductive rubber is taken as an example, but when the sidewall rubber is a non-conductive rubber, the conductive portion extends from the bottom surface of the cap portion to a position exposed to the ground plane. It may be formed by being spirally arranged.

  Such a cap part 150 and the conductive part 152 are manufactured as follows. In two shots using two rubber extruders, as shown in FIG. 5, one extruder extrudes the first ribbon Rb1 made only of the non-conductive rubber G1, and the other extruder is shown in FIG. As shown, this is a dual extruder that extrudes a strip-shaped non-conductive rubber G2 and a second ribbon Rb2 of the conductive rubber G3 covering one side of the non-conductive rubber G2. Then, by alternately winding the first ribbon Rb1 and the second ribbon Rb2, the cap portion 150 is formed by the non-conductive rubber G1 and G2, and the conductive portion 152 is formed by the conductive rubber G3. . According to such a manufacturing method, the conductive portion 152 can be easily formed.

  Even if comprised in this way, there exists an effect similar to the said this embodiment. Further, since the belt-like conductive rubber has a length in the tire width direction, a part of the tire side end portion is partitioned inside the tire by a conductive rubber having a rubber hardness different from that of the cap portion 150. . Therefore, similarly to the present embodiment, only by providing such a conductive portion, the rigidity of the side end portion of the cap portion can be changed as compared with the case where there is no conductive portion, and can be set to a desired rigidity. Noise can be reduced through appropriate stiffness settings. Further, in the cross section of the tire meridian, the conductive portion 152 is separated from the portion P2 exposed to the grounding surface and the portion P3 reaching the side end surface 150a of the cap portion 150 by the nonconductive rubber forming the cap portion 150. Further, the volume of the conductive rubber is suppressed, and further rolling performance can be pursued.

  (6) In addition, in the said embodiment, as shown to FIGS. 1-4, although site | part P1 * P2 exposed to a ground surface is one place among the electroconductive parts 52 and 152, FIG. As shown in c), the conductive portions 52 and 152 may be exposed at a plurality of locations on the ground plane. 6 (a) and 6 (b), it can be said that one or more extending portions 52b are arranged on the inner side in the tire width direction WD from the ground contact end E. According to such a structure, manufacture becomes easy compared with the said embodiment. 6A is a modified example corresponding to FIG. 2, FIG. 6B is a modified example corresponding to FIG. 3, and FIG. 6C is a modified example corresponding to FIG. It is.

  In order to specifically show the configuration and effects of the present invention, the following evaluations were performed on the following examples.

(1) Energization performance (electric resistance value)
A predetermined load was applied to the tire mounted on the rim, and an applied voltage (500 V) was applied from the shaft supporting the rim to the metal plate to which the tire contacts the ground, and the electrical resistance value was measured.

(2) Rubber hardness The rubber composition was vulcanized at 150 ° C for 30 minutes, and the rubber hardness of the vulcanized rubber at 23 ° C was measured according to JISK6253.

(3) Rolling resistance The rolling resistance was measured and evaluated with a rolling resistance tester. The result of Comparative Example 1 is evaluated as 100, and the larger the value, the better the rolling resistance.

(4) Uniformity LFV (Lateral Force Variation) was measured based on the test method specified in JIS D4233 to evaluate tire uniformity. Specifically, the amount of change in the lateral force generated when the tire is rotated against the rotating drum so that a load of 640 N is applied to the tire with an air pressure of 200 kPa and the distance between both axes is kept constant. Was measured. The result of Comparative Example 1 is evaluated as 100, and the larger the numerical value, the better the uniformity in the horizontal direction.

(5) Noise level (low frequency region and high frequency region)
The test tire was adjusted to an air pressure of 200 kPa using a standard rim, the same tire was mounted on all wheels of a domestic 2000 cc passenger car, and the noise was measured with a sound level meter during steady running at 60 km / h. Of the measured noise, the 80 to 160 Hz component was defined as noise in the low frequency region, and from the measured noise, the 250 to 500 Hz component was defined as noise in the high frequency region. The result of Comparative Example 1 is evaluated as 100, and the noise is reduced as the numerical value increases.

(6) Uneven wear The tire was attached to a live-action photograph and traveled 12,000 km on a general road. Comparison was made by the ratio of wear amount between the equator part (center part) of the tread part after running and the shoulder part (near the ground contact end). The closer the ratio is to 1.0, the more uniform wear occurs. The ratio of Comparative Example 1 is evaluated as 100. The smaller the numerical value is, the farther the ratio is from 1.0 and the uneven wear is. The larger the numerical value is, the closer the ratio is to 1.0 and uniform wear.

(7) Crack resistance performance The tire was irradiated with ozone, and the size and depth of the cracks produced were evaluated. The result of Comparative Example 1 is evaluated as 100, and the larger the value, the better the crack resistance performance.

Comparative Example 1
A tire having a size of 195 / 65R15 was produced by placing conductive rubber at a position covering both side end portions of the cap portion 50 of non-conductive rubber to form a tread rubber.

Example 1
For the tire of Comparative Example 1, conductive portions 52 were provided inside the side wall portions of the cap portion 50. The rubber hardness of the conductive part 52 was set lower than the rubber hardness of the cap part 50. Otherwise, the tire was the same as the tire of Comparative Example 1.

Example 2
The conductive portion 52 was provided only on the side end portion on the inner side of the vehicle body among the paired side end portions on both sides of the tire width direction WD of the cap portion 50. Otherwise, it was the same as Example 1.

Example 3
The rubber hardness of the conductive part 52 was made higher than the rubber hardness of the cap part 50. Otherwise, it was the same as Example 1.

  From Table 1, it can be seen that in Examples 1 to 3, the rolling resistance is effectively reduced as compared with Comparative Example 1.

  About energization performance, in comparative example 1 and Examples 1-3, it turns out that energization performance is secured appropriately.

  In addition, with respect to uniformity, the conductive portion 52 is provided at both side end portions of the cap portion 50 as compared with the second embodiment in which the conductive portion 52 is provided only at one side end portion of the cap portion 50. Since Example 1 is better, it can be seen that it is preferable to provide the conductive portions 52 on both sides in the tire width direction.

  Regarding the noise, the first embodiment in which the conductive portion 52 having a hardness lower than that of the cap portion 50 is provided in comparison with the comparative example 1 in which the cap portion 50 does not have the conductive portion 52. I understand. Similarly, it can be seen that the noise in the high frequency region is reduced in Example 3 in which the conductive portion 52 having a hardness higher than that of the cap portion 50 is provided with respect to Comparative Example 1.

DESCRIPTION OF SYMBOLS 1 ... Bead part 2 ... Side wall part 3 ... Tread part 4 ... Carcass layer 6 ... Side wall rubber 5 ... Tread rubber 50 ... Cap part 50a ... Side end surface 50b of cap part ... Bottom face 51 of cap part ... Base parts 52, 152 ... conductive portion 52a ... conductive path 52b ... extended portion RD ... tire radial direction WD ... tire width direction

Claims (3)

Between a pair of bead portions, a sidewall portion extending outward in the tire radial direction from each of the bead portions, a tread portion connected to an outer end in the tire radial direction of each of the sidewall portions, and between the pair of bead portions A pneumatic tire comprising: a toroidal carcass layer provided; a sidewall rubber provided outside the carcass layer in the sidewall portion; and a tread rubber provided outside the carcass layer in the tread portion. Because
The tread rubber is formed of a non-conductive rubber and forms a contact surface, a base portion provided on the inner side in the tire radial direction of the cap portion, and a pair of both ends of the cap portion in the tire width direction. The ground contact surface and the cap portion in a tire meridian cross-section passing through the inside of the cap portion while avoiding a position provided on at least one side end portion of the side end portions and covering the surface of the cap portion forming the ground contact surface A conductive portion having a shape connecting the side end surface or the bottom surface of
The conductive portion has an extending portion that branches from a conductive path connecting the grounding surface and a side end surface or a bottom surface of the cap portion and extends outward in the tire width direction, and forms a non-conductive rubber. A pneumatic tire characterized in that it is made of a conductive rubber having a rubber hardness different from that of the pneumatic tire. Between a pair of bead portions, a sidewall portion extending outward in the tire radial direction from each of the bead portions, a tread portion connected to an outer end in the tire radial direction of each of the sidewall portions, and between the pair of bead portions A pneumatic tire comprising: a toroidal carcass layer provided; a sidewall rubber provided outside the carcass layer in the sidewall portion; and a tread rubber provided outside the carcass layer in the tread portion. Because
The tread rubber is formed of a non-conductive rubber and forms a contact surface, a base portion provided on the inner side in the tire radial direction of the cap portion, and a pair of both ends of the cap portion in the tire width direction. Provided on at least one side end of the side ends, passing through the inside of the cap part while avoiding the position covering the surface of the cap part forming the grounding surface, or the side end face of the cap part or A conductive portion that electrically connects the bottom surface,
The conductive portion includes a strip-shaped conductive rubber having a rubber hardness different from that of the nonconductive rubber forming the cap portion, and the conductive rubber is exposed to the grounding surface from a side end surface or a bottom surface of the cap portion. It is in a state of being arranged in a spiral manner around the tire axis up to a position, and in the tire meridian cross section, the non-conductive rubber forming the cap portion exposes the portion exposed to the ground contact surface and the side end surface of the cap portion or A pneumatic tire characterized in that a part reaching the bottom is divided. The pneumatic tire according to claim 1, wherein the conductive portion is provided on one side in the tire width direction and on the other side in the tire width direction.